Recombinant SARS-CoV-2, RBD Protein (Delta Plus, B1.617.2.1, AY.1, India Variant) - 500 µg

The three clades of lineage B.1.617 are B.1.617.1, B.1.617.2, and B.1.617.3, shown in chronological order of detection. This delta plus variant of SARS-CoV-2 (also known as B.1.617.2.1 or AY.1) emerged in India and is spreading in a number of countries.1 The RBD mutation is K417N, L452R, T478K, indicating an extra mutation which distinguishes it from the regular delta variant. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), is an enveloped, single-stranded, positive-sense RNA virus that belongs to the Coronaviridae family 2. The SARS-CoV-2 genome, which shares 79.6% identity with SARS-CoV, encodes four essential structural proteins: the spike (S), envelope (E), membrane (M), and nucleocapsid protein (N) 3. The S protein is a transmembrane, homotrimeric, class I fusion glycoprotein that mediates viral attachment, fusion, and entry into host cells 4. Each ~180 kDa monomer contains two functional subunits, S1 (~700 a.a) and S2 (~600 a.a), that mediate viral attachment and membrane fusion, respectively. S1 contains two major domains, the N-terminal (NTD) and C-terminal domains (CTD). The CTD contains the receptor-binding domain (RBD), which binds to the angiotensin-converting enzyme 2 (ACE2) receptor on host cells 4-6. Although both SARS-CoV and SARS-CoV-2 bind the ACE2 receptor, the RBDs only share ~73% amino acid identity, and the SARS-CoV-2 RBD binds with a higher affinity compared to SARS-CoV 4,7. The RBD is dynamic and undergoes hinge-like conformational changes, referred to as the “down” or “up” conformations, which hide or expose the receptor-binding motifs, respectively 8. Following receptor binding, S1 destabilizes, and TMPRSS2 cleaves S2, which undergoes a pre- to post-fusion conformation transition, allowing for membrane fusion 9,10.